Potent human MC1 receptor antagonist (IC50 = 17 nM). Also partial agonist at human MC3 and MC5 receptors (EC50 values are 59 and 1300 nM, respectively). Exhibits binding affinity for A375 melanoma cells in vitro. Reverses morphine-induced hyperalgesia in female mice, with no effect in male mice. γMSH analog. MW (observed): 1347.51.